The invention relates to a sterilization container having a valve arrangement which permits a media exchange inside a sterilizer right into the vacuum drying phase and closes in the last ventilation phase, so that the vacuum prevailing at this instant in the container interior is maintained and the container remains hermetically sealed, the valve arrangement having a valve body subjected to the flow pressure.
Such sterilization containers, as described, for example, in DE 41 11 075 C2, have the advantage that the material to be sterilized can be kept in the container for a prolonged period without the risk of contamination, since the external atmospheric pressure keeps the container hermetically closed until ventilation is effected at random. The valve body is under spring preloading, which keeps the valve in the open position until the pressure in the sterilizer increases in the last ventilation phase and presses the valve body onto its valve seat, as a result of which the vacuum prevailing in the container at the moment of closing is maintained.
In the valve arrangement, however, the valve body must be reliably prevented from being pressed onto the valve seat prematurely by the inflowing steam, since otherwise no reliable sterilization could take place and the container could even possibly implode. It has been found that the spring preloading of the valve body in the open position cannot reliably prevent premature closing in particular when this valve body subjected to the pressure of the flow medium has a considerable surface extent. The risk of premature closing is there, depending on the load, due to the high inflow velocities. The greater the amount of material to be sterilized which is in the container, the greater is the steam consumption required in the same time. The sterilizer is subjected to a pressure increase controlled with respect to time, i.e. the pressure increases constantly in the environment of the container, and it also penetrates into the container, in which case immediate condensation takes place (gaseous-liquid phase transition releases heat). Accordingly, the container must be “resupplied” with steam, but this steam immediately condenses again, until the heating achieved by constant condensation leads to a situation in which steam can no longer condense.
Thus, if an empty container is sterilized, hardly any more steam is required on the “inside” as on the “outside” (in order to reach 134° C.): the valve is then not substantially loaded with flow pressure.
If a load is sterilized, substantially more steam is “consumed” on the inside—depending on the total weight and the heat capacity of the load: thus substantially more steam—in the same time predetermined by the sterilizer—must therefore [lacuna] through the valve gap than in the empty state. In the case of larger loads, there is therefore the risk of slamming.
In the sterilization containers of the generic type, the valve control is expediently effected via at least one temperature sensor with hysteresis behavior. This temperature sensor may be provided with a snap-disk arrangement, as described in DE 41 11 075 C2. Such a sterilization container, after opening, and after removal of the sterile material, is again available for a renewed sterilization operation without manual valve actuation being necessary. In order to ensure this, the temperature sensor, after removal of the sterilization container from the sterilizer, must automatically switch back again into the original state. In temperature sensors having a snap-disk arrangement, the switching-back is effected by the hysteresis behavior of the thermobimetal. The temperature sensors with snap disks, but also other temperature sensors, are therefore designed in such a way that the switching-back is effected within a temperature range in which the vacuum valve controlled by the sensor is reliably closed, i.e. the switching-back must not be effected before completion of the ventilation phase. In snap-disk arrangements, a temperature of 30 to 50° C. is generally assumed as switch-back temperature, i.e. a temperature which is normally not achieved until after removal from the sterilizer and after cooling of the sterilization container to room temperature.
However, it has been found that these switching temperatures of preferably 35 to 40° C., under certain circumstances, may already be reached during a drying phase inside the sterilizer. This premature cooling may occur during the sterilization of heavy steel loads, since these steel loads produce very large condensate quantities, as a result of which the sensor arrangement may be wetted with condensed steam. If vacuum drying now starts, condensate is re-evaporated, resulting in energy consumption and cooling at those locations where evaporation of the moisture occurs. If such cooling is effected in the region of the temperature sensors, the end of the sterilization operation is simulated, and premature switching-back may be effected, which would result in incorrect switching of the vacuum valve.